Keith Morton Security, a private security firm that does mostly security work for private buildings, is based in Upper Changi Road and employs about 90 staff. Mr Ridhuan, who was last deployed at a condominium complex in the Holland Road area, was given his marching orders on Monday, the day after he wrote the post.

Mr Morton added that the offensive comment was brought to his notice by a close friend, and he decided immediately that he had to let the security officer go to protect the company's name.

"It was my own decision and nobody asked me to do it," he stressed.

PM Lee's Mother's Day wishes were posted on Facebook with an old black-and-white photograph of himself, his brother and his late mother.

In the post, he thanked all mothers, writing: "One day is simply not enough to thank mothers for their unconditional love and untiring care."

Within two hours, it drew more than 22,300 likes.

Mr Ridhuan removed his obscene 13-word entry, posted under the moniker GrizzlyBear Ridhuan Abdullah, after he was fired.

He declined to comment when contacted yesterday.

Facebook users must agree not to intimidate or harass others.

Lawyers who were contacted said freedom of expression must be within the limits of decency, and that people who make such comments can be taken to task.

"Obscenities online can be the subject of an offence or a civil case. I agree that the authorities should check or discourage this," said lawyer B.J. Lean.

vijayan@sph.com.sg

This article was published on May 15 in The Straits Times.Get a copy of The Straits Times or go to straitstimes.com for more stories.